Pulverizing apparatus

ABSTRACT

This invention relates to an apparatus for pulverizing quick lime into a slurry form. It has a vertical shell and a rotary shaft mounted in the shell. An agitating layer and a pulverizing layer are formed in the shell at its upper and lower portions, respectively. The material fed from top of the shell is agitated and melted into smaller particles in the agitating layer and then pulverized into fine particles in the pulverizing layer. The fine particles are discharged from a top or middle of the shell. A discharge pipe is provided so as to extend upwardly from the discharge port at the middle of the shell. An agitator may be provided in the discharge pipe. The material to be pulverized is prevented from going from the inlet directly to the outlet without passing through the pulverizing layer.

TECHNICAL FIELD

The present invention relates to a pulverizing apparatus for pulverizinga material into a slurry form.

BACKGROUND ART

As a method of desulfurizing exhaust gas, it is known to spray thereonslaked lime in the form of slurry. A conventional apparatus forproducing such slaked lime is shown in FIG. 5. This apparatus comprisesa vertical shell 1 filled with a pulverizing medium b and a screw shaft2 extending vertically in the shell 1. A quick lime material s and waterare fed into the shell from its top. The material s is pulverized by thefriction with the pulverizing medium b and between its own particleswhile reacting with water such that it turns into slaked lime in theform of slurry.

Since solid impurities such as calcium carbonate and gravel contained inthe material are also pulverized into fine particles, the material turnsinto slaked lime c in the form of slurry containing the above fineparticles of impurities and continuously flows out through an outlet 3at the upper part of the shell 1 into a settling separator 4. It isnecessary to pulverize the impurities into fine particles in order toprevent a nozzle from clogging during the above-described spraying. Inthe drawing, letter P indicates a circulating pump for the settledproduct.

But during the above-described pulverizing operation, any quick limematerial s which is too large to be mixed into a layer of thepulverizing medium b tends to flow directly to the outlet 3 from theinlet. Such unpulverized large-diameter particles are liable to flowthrough the settling separator 4 and mix into the end product d, thuslowering its commercial value. The larger the ratio of the quick limematerial to water, the more remarkable this phenomenon will be. This isbecause the viscosity of the slurry increases and the separationefficiency by settling decreases as the concentration of the material sgrows. Thus, such a conventional apparatus has to be operated underlow-concentration conditions. This will lower the production efficiency.

Meanwhile, it is known that a soluble material such as soil stuck tosolid pieces such as stones serves to bind them together. If the solublematerial melts, the solid pieces will separate. As to the quick limematerial s, it contains impurities having a soluble material such asquick lime and the like stuck thereto. If the quick lime and the likemelts as a result of reaction, the diameter of its particles willdecrease. In other words, the particle diameter of the quick limematerial can be reduced and thus it can easily mix into the layer ofpulverizing medium b by promoting its reaction and melting.

An object of the present invention is to enhance the reaction andmelting of quick lime and to smoothly mix the material to be pulverizedinto the pulverizing layer by agitating the material in a verticalshell.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided apulverizing apparatus comprising a vertical shell for containing aliquid such as water and a pulverizing medium, and a rotary shaftrotatably mounted in said vertical shell and having a plurality ofagitating vanes mounted in an upper portion thereof to form an agitatinglayer and having a screw in an lower portion thereof to form apulverizing layer with the pulverizing medium.

The agitating vane should preferably be shaped to produce a downwardcurrent of the material.

The apparatus according to the present invention has a material inletdisposed at a top of the vertical shell and a product outlet disposed atthe top or middle of the vertical shell. A discharge pipe may beprovided so as to extend upwardly from the outlet. The discharge pipemay be provided with a gate for determining the water level in thevertical shell. Also, an agitator should be provided in the dischargepipe.

The material to be pulverized may be any material which reacts withwater or other liquid and melts into a slurry form, such as quick limeand dolomite.

With the pulverizer having a construction as described above, when thematerial to be pulverized is fed into the shell from its upper part withthe rotary shaft in rotation, it will be agitated and melted whilesettling down in the agitating layer. By arranging the agitating bladesso as to form a downward current, the material to be pulverized willreliably mix into the agitating layer and will be agitated. By promotingthe melting, the material can turn rapidly into slurry and its particlediameter can be reduced, because the material acting as a binder melts.If for example the material to be pulverized is quick lime, not onlywill the above-mentioned action be promoted, but reaction of the quicklime will also be promoted. Thus the material can be turned into slurrymore rapidly and the particle diameter can be reduced still further.

As described above, the particle size of the material to be pulverizedis reduced while it settles down in the agitating layer. The particleswhich have been pulverized into a sufficiently small size will beentrained in a current toward the outlet, whereas the particles toocoarse to be entrained in this current will be mixed in the pulverizinglayer and pulverized into fine particles.

This operation is carried out in the agitating layer and the pulverizinglayer in a continuous and complex manner so that the material to bepulverized can leave the shell in a slurry form.

If the inlet port is formed in the upper part of the vertical shell, theoutlet discharge port is formed in the middle level of the shell, adischarge pipe is provided so as to extend upwardly from the outletport, and the discharge pipe is formed with a gate for determining theliquid level in the vertical shell, such that the material to bepulverized will flow through the agitating layer without failure. Thus,the agitating efficiency is improved.

Further, by the provision of an agitator in the discharge pipe, thelatter will be prevented from getting clogged with the material to bepulverized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are schematic views of four embodiments of the pulverizingapparatus according to the present invention; and

FIG. 5 is a schematic view of an example of a prior art apparatus.

DETAILED DESCRIPTION OF

Embodiment 1

As shown in FIG. 1, a rotary shaft 11 is provided along the central axisof a vertical cylindrical shell 10. The rotary shaft 11 is provided atits upper part with radially extending agitating vanes 12 arranged ataxially equal intervals. An agitating layer (or slaking layer) A isformed in the shell 10 at its upper portion. The agitating vanes 12 areinclined forwardly with respect to the direction of rotation so thatthey will form a downward current while in rotation. The angle ofinclination of the agitating vanes 12 may be determined suitablyaccording to the application. They may be arranged so that their widthwill extend in the axial direction of the rotary shaft 11, instead ofbeing inclined.

Also, the rotary shaft 11 is provided at its lower portion with a screw13 and a pulverizing layer B filled with pulverizing medium b is formedin the shell at its lower portion. Accordingly, when the quick limematerial s is fed into the reach of the agitating vanes 12 from theupper part of the shell 10 together with water, it will be agitated andwill react with the water in the agitating layer A. Thus, the slakedlime melts and turns into slurry and the material s is pulverized. Inthe material, the particles which have been pulverized to a sufficientlysmall size are entrained in a current toward an outlet port 14 which isto be described later, whereas the remaining portion of the material s(the lime left unreacted and the impurities) will settle down into thepulverizing layer B where it will be pulverized into fine particles bythe friction with the pulverizing medium b and the friction between itsown particles. The particles thus pulverized will rise in the shell withthe upward current.

The shell 10 has an outlet (discharge) port 14 formed at a side thereofopposite the inlet port for the quick lime material. The slurry ofslaked lime c containing the particles carried on the upward currentwill flow through the outlet port 14 into a settling separator 15, inwhich the mixed coarser particles mixed (the unreacted lime andimpurities) will settle, whereas the remainder will overflow theseparator so as to be taken out as the end product d. The coarserparticles which have settled are carried back to the shell 10 by a pumpP.

The volume ratio between the agitating layer A and the pulverizing layerB should be determined suitably through experiments. In the drawings,letter M indicates a driving means.

Embodiment 2

In the embodiment shown in FIG. 2, the outlet port 14 is formed in theshell 10 at the middle level thereof. A discharge pipe 16 is provided toextend obliquely upwardly from the outlet port 14. In the discharge pipe16, there is provided an agitator 17 to prevent the pipe 16 from gettingclogged with a slurry of slaked lime c. This is especially effective forpulverization under high-concentration conditions. The outlet port 14may be covered with a screen to prevent the pulverizing medium b fromflowing out.

The discharge pipe 16 is formed in its upper part at the side thereoffacing the settling separator 15 with an opening 25. This opening isclosed with an adjustable plate 18 which is axially movably mounted soas to be fixed at a desired position. The top edge of this adjustableplate 18 serves as a gate 19. By moving the adjustable plate 18, thelevel of the gate 19 and thus the liquid level in the shell 10 aredetermined. The adjustable plate 18 may be fixed in position by bolts orthe like. In the settling separator 15, there is provided a plate 20extending downwardly beyond the level of its outlet port 26 to preventthe slurry from going directly to the outlet 26. The slaked lime willthus remain in the settling separator for a longer period of time. Thisanti-shortcircuitting plate 20 has an adjustable position.

In this embodiment, the material s to be pulverized (quick limematerial) is sure to pass through the agitating layer A. This promotesthe reaction and melting of the material. Also, the downward currentformed in the agitating layer A allows the material to settle downsmoothly and allows the coarser particles to mix smoothly into thepulverizing layer B.

Embodiment 3

In the embodiment shown in FIG. 3, the single agitator 17 used in theembodiment 2 is replaced with two agitators 17a and 17b. The smalleragitator 17b is provided near the outlet port 14 to agitate the materialnear the outlet port where clogging is most likely to take place. Thenumber of agitators 17 is not limited to two. They may be provided inany appropriate number.

Embodiment 4

In the embodiment shown in FIG. 4, there are provided two verticalshells 10, one having the agitating layer A and the pulverizing layer Band the other having only the pulverizing layer B. With thisarrangement, the pulverizing time can be extended. A communicating hole21 formed between the shells 10 is covered with a screen 27 to preventthe pulverizing media b in the respective shells 10 from passing throughthe hole 21 and mixing together. Three or more shells 10 may be used.

Industrial Application

The apparatus according to the present invention can produce slaked limein a slurry form with good efficiency and the slaked lime obtained canbe used for the desulfurization of exhaust gas. It can also be melted inwater or other liquid for the production of other material.

What are claimed are:
 1. A pulverizing apparatus comprising a verticalshell for containing material including a liquid and a pulverizingmedium, said shell having a top inlet, and a rotary shaft having aplurality of agitating vanes mounted at an upper portion thereof to forman agitating layer and having a screw at a lower portion thereof to forma pulverizing layer;wherein said agitating vanes are shaped to produce adownward current of the material; and wherein the material to bepulverized is fed into said shell through said top inlet, a dischargeport being formed at a middle portion of said shell, and a dischargepipe being provided so as to extend upwardly from said discharge port.2. A pulverizing apparatus as recited in claim 1, wherein said dischargepipe is provided with a gate for adjusting the liquid level in saidvertical shell.
 3. A pulverizing apparatus as recited in claim 1,wherein an agitator is mounted in said discharge pipe.